The skeletal system includes many long bones that extend from the human torso. These long bones include the femur, fibula, tibia, humerus, radius and ulna. These long bones particularly are exposed to trauma from accidents, and as such often are fractured during such trauma and may be subject to complex devastating fractures.
Automobile accidents, for instance, are a common cause of trauma to long bones. In particular, the femur and tibia frequently fracture when the area around the knee is subjected to a frontal automobile accident.
Often the distal end or proximal portions of the long bone, for example the femur and the tibia, are fractured into several components and must be realigned. Mechanical devices, commonly in the forms of pins, plates, screws, nails, wires and external devices are commonly used to attach fractured long bones. The pins, plates, wires, nails and screws are typically made of a durable material compatible to the human body, for example titanium, stainless steel or cobalt chromium.
Fractures of the long bone are typically secured into position by at least one of three possible techniques or methods.
The first method is the use of intramedullary nails that are positioned in the intramedullary canal of those portions of the fractured bone.
A second method of repairing fractured bones is the use of internal bone plates that are positioned under the soft tissue and on the exterior of the bone and that bridge the fractured portion of the bone.
Another method of securing fractured bones in position is the use of external fixators. These external fixators have at least two general categories. In one category, the fixator is generally linear, with a first portion of the fixator to connect to a first fracture segment of the bone and a second fracture segment of the fixator to connect to a second fracture segment of the bone. A first series of bone screws or pins are first connected to the fixator and then to the first fracture segment of the bone. Then a second series of screws or pins are connected to the fixator and then to the second fracture segment of the bone, thereby securing the first fracture segment of the bone to the second fracture segment of the bone.
A second method of external fixation is through the use of a ring type fixator that uses a series of spaced-apart rings to secure the bone. For example, an upper ring and a lower ring are spaced apart by rods. A plurality of wires is placed through the long bone and connected on each end of the long bone by the ring. The wires are then tensioned much as a spoke in a bicycle are tightened, thereby providing for a rigid structure to support the first fracture segment portion of the bone. Similarly, a plurality of wires are positioned through the second fracture segment of the bone and are secured to and tensioned by the lower ring to provide a rigid fixation of the second fracture segment of the bone bridging the fracture site.
There are a variety of devices used to treat femoral fractures. Fractures of the neck, head or intertrochanter of the femur have been successfully treated with a variety of compression screw assemblies which include a compression plate having a barrel member, a lag screw and a compressing screw. The compression plate is secured to the exterior of the femur and the barrel member is inserted into a predrilled hole in the direction of the femoral head.
The lag screw which has a threaded end and a smooth portion is inserted through the barrel member so that it extends across the break and into the femoral head. The threaded portion engages the femoral head. The compressing screw connects the lag screw to the plate. By adjusting the tension of the compressing screw the compression (reduction) of the fracture can be adjusted. The smooth portion of the lag screw must be free to slide through the barrel member to permit the adjustment of the compression screw.
Subtrochanteric and femoral shaft fractures have been treated with the help of intramedullary rods, which are inserted into the marrow canal of the femur to immobilize the femoral parts involved in fractures. A single angled cross-nail or locking screw is inserted through the femur and into the proximal end of the intramedullary rod. In some varieties, one or two screws may also be inserted through the femoral shaft and through the distal end of the intramedullary rod. These standard intramedullary rods have been successfully employed in treating fractures in lower portions of the femoral shaft.
Trochanteric nails for use in preparing femoral neck fractures utilize a screw in the form of, for example, a lag screw. The lag screws have several different problems in use that are generally related to the lag screw not remaining in the proper position with respect to the intramedullary nail during the operating life of an implant. For example, the lag screw may cut proximally through the femoral neck and head, causing the neck and head to move out of its operating position in cooperation with the acetabulum. Such a movement may render the patient non-ambulatory. Another issue that may occur with lag screws is medial migration of a lag screw through the femoral head and into the pelvic cavity. A further issue with an intramedullary nail lag screw is lateral migration or lateral pullout of the screw from the long bone.
Yet another problem with lag screws in trochanteric nail applications is the problem of neck collapse. Early after the implantation of the trochanteric nail, for example, at the first weight-bearing instance of the patient, the head of the femur may move distally due to a phenomenon known as neck collapse. If the lag screw does not capture enough cancellous bone in the femoral neck, the neck and head may move laterally causing the phenomenon known as neck collapse and creating a leg length and other issues for the patient.
Medial migration is only one of many problems that occur with a fastener for use with orthopaedic prosthetic components. The design of fasteners in cancellous and/or osteoporotic bone must deal with parameters such as pull-out forces, installation torque requirements, stripping of the bone, migration and others.
The proximal femoral fractures, for example, those around the lesser trochanter, greater trochanter, and femoral neck have been successful treated with a variety of compression screw assemblies and intramedullary rods. The intramedullary rods are inserted into the narrow canal of the femur to immobilize the femur parts involved in the fracture. Typically, a single screw is inserted through the femur and the proximal end of the intramedullary rod. Alternatively, a second screw may be inserted through the femur and into the proximal end of the intramedullary rod to prevent rotation of, for example, the neck and head of the femur.
One of the earliest intramedullary devices introduced in the United States was the Grosse-Kempf nail manufactured by Howmedica Company of Rotherudge, N.J. The Grosse-Kempf nail includes a threaded hole in the intramedullary rod for receiving an interlocking screw. The fully threaded screw cannot freely slide in order to permit the compression found in typical compression screw assemblies.
Another prior art device is in the form of Zickel™ nail (U.S. Pat. No. 3,433,220). The Zickel nail is a solid intramedullary nail having a single proximal tri-flangle cross-nail which is inserted into the direction of the femoral head. The solid cross-section does not permit the nail to be introduced over a guide rod. Thus, the nail is prevented from being used for comminuted and distal fractures of the femur because the closed surgical technique cannot be practiced. In addition, adequate compression cannot be achieved due to the requirement to lock cross-nail.
Yet another prior art device is in the form of the Russell-Taylor™ interlocking nail manufactured by Richards Medical Company of Memphis, now Smith, Nephew, and Richards. The Russell-Taylor nail similarly requires a fully threaded locking screw and therefore does not permit sliding of the screw relative to the intramedullary rod.
Yet a further prior art device is in the form of the Gamma™ nail is manufactured by Stryker-Howmedica. The Gamma nail provides for sliding compression of the lag screw through the use of a smooth shaft. The Gamma nail stops rotation of the lag screw by means of a set screw through the proximal portion of the intramedullary nail.
A further prior art device in the form of the Ace Trochanteric™ nail manufactured by DePuy Orthopaedics, Inc. provides for means of stopping rotation of the femoral head in an unstable fracture pattern by the use of a second threaded screw in the femoral head. The lag screw is permitted to rotate freely within the nail.
In unstable femur fractures, stability is necessary to facilitate proper healing of the bone. The femur fractures may be a greater trochanteric to lesser trochanteric fracture, or a fracture of, for example, the neck of the femur. In compound fractures, the bone may be fractured at more than one fracture site. Such multiple fractures are instable and the proper healing of such fractures is difficult. Axial and rotational stability of such fractures may also be an issue. The present invention is an attempt to address at least some of the aforementioned issues.
The present invention is directed to alleviate at some of the aforementioned concerns with orthopaedic fasteners.